Your reports can be off if you set up your Analytics E-commerce tracking in the middle of the day.

Keep in mind that all the transactions executed before the implementation of the Analytics Tracking do not appear in the Analytics Reports. Obviously these transactions appear in the shopping cart reports.

The Google Analytics Ecommerce Tracking code may not properly set up.

The reversed/cancelled transactions don’t appear in the reports. The transactions with a value of 0 are not reported